| Title | Silicification Process in the Reservoir Rocks of the Los Humeros Geothermal Field, Mexico |
|---|---|
| Authors | Georgina IZQUIERDO MONTALVO, Alfonso ARAGON, Wilfred ELDERS, Candy JIMENEZ, Rosaura OCAMPO, Rafael Gomez |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Los Humeros, petrology, silicification, quartzification |
| Abstract | The Los Humeros geothermal field (LHGF) is the third geothermal resource in Mexico administrated by the CFE. At present is one of the two main topics of the GEMex project between Mexico and European Community. The LHGF is characterized by low permeability reservoir rocks. Deep fluid movement exist trough a layer between two andesitic units, known as vitreous tuff. The main water-rock interaction occurs in the upper andesitic unit. However, the layer in between the two andesitic units has suffered, in some areas of the reservoir, a total silicification process (referred as quartzification since the dominant crystalline phase is quartz). We assume that this quartzification process is the result of leaching of the tuff or of the andesite due to the effects of a low pH fluid. This process occurs when condensation of the steam phase is mixed with deep volatile species forming a low pH fluid that reacts with the rock leaving a silicified material. As the fluids reacts with the rocks, it becomes neutral. The quartzification process has been studied by petrography, XRD and MEB. The highest quartzification is observed in some wells between 1800 and 2100 m depth. It is composed almost all by microcrystalline quartz and plagioclase with low amount of chlorite, pyrite and muscovite. The highest measured permeability in the reservoir rocks corresponds to the highest quartzified strata. This unit correlates to the relative highest circulation losses at depth and correspond to the lithological unit identified as Unit 7. |